On Tue, 14 Oct 2008 09:48:42 +0200 Iljitsch van Beijnum <[EMAIL PROTECTED]> wrote:
> On 13 okt 2008, at 22:59, Thomas Narten wrote: > > > So, clients will retransmit about once every 2 minutes. > > But they'll transmit packets more frequently initially. > > >> This is unnecessary multicast traffic that could easily affect wifi > >> performance because on 802.11 multicasts are generally sent at the > >> lowest supported speed. > > > But let's not forget, Neighbor Discovery also uses IP multicast. So, > > if multicasts are problematical they are probably already > > problematical just for ND. Right? > > It's not a question of "problematic yes/no". More multicasts means > less performance for other stuff. Obviously ARP and ND already > generate multicasts, as do various discovery systems such as netbios > and multicast DNS. I believe this is an important reason why 802.11g > performance in the plenaries during IETF meetings is so bad, but I > don't have hard figures to support this. > Well, that seems to me to be a layer 2 design problem, and so would be best solved at layer 2, not at layer 3. The solutions to this problem are well known. Divide the layer 2 domain up into subdomains, separated by routers, or, if it is necessary to have a large layer 2 domain, then move to a non-broadcast multiaccess (NBMA) layer 2 model, and then use NHRP to overcome the lack of layer 2 multicast support. There's even acknowledgement in the NHRP RFC that the solution could be used in BMA networks: "Note that while this protocol was developed for use with NBMA subnetworks, it is possible, if not likely, that it will be applied to BMA subnetworks as well. However, this usage of NHRP is for further study." (RFC2332) The IETF / lecture hall scenario could probably be fairly easily solved by having NRHP stacks on the end-nodes, and information in the RAs from the local routers supplying the NHRP server(s) to use. How have the 3GPP people solved this problem? It seems to me to be quite a similar one. I'd assume they're not allocating out /64s for each phone to phone tower point to point connection, so that starts to imply their link layers are NBMA too. Regards, Mark. -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
